Lattice trends in Ti(5)Si(3)Z(x) (Z=B,C,N,O and 0 < x < 1)

Several Ti(5)Si(3)Z(x) compositions (Z=boron, carbon, nitrogen and oxygen) were synthesized by are-melting. Powder X-ray diffraction indicates the mat erials maintain the Mn5Si3-type structure of the binary compound Ti5Si3. Ca lculated cell constants were correlated to ternary composition based on che mical analysis. Nitrogen and oxygen additions to Ti5Si3 promote a cell volu me decrease, while boron additions promote a cell volume increase. Carbon a dditions cause a decrease in the a-cell constant and an increase in the c-c ell constant with a concomitant cell volume increase. Room temperature X-ra y single crystal structural analysis was performed on one composition for e ach ternary addition. Each analyzed composition has the P6(3)/mcm space gro up (No. 193) with the Mn5Si3-type structure. The ternary addition occupies the normally vacant interstitial site at the center of the trigonal antipri sms of titanium (Ti2) atoms (Ti(6)Z polyhedra), located in chains at the co rners of the hexagonal unit cell. Bonding between the interstitial atoms an d the titanium (Ti2) atoms in the Ti(6)Z polyhedra is indicated by a decrea se in the Ti2-Ti2 and Ti2-Z atomic separations. (C) 2000 Elsevier Science S .A. All rights reserved.